*Snapshot*"And after I took that picture, I heard a loud and muffled scream of 'YOU LITTLE PERVERT!!' ... I'm still wondering if that purple stuff was a thing with the fur or she just got paintballed or something else.."

"in the moon"...I have a new headcanon!Maybe Luna/NM's physical form was taken away from her temporarily for a millenium, and her conscious/mind/spirit/fuckitidontcare was put inside of the moon by some strange power of blah, hence the reason why you could see the moon with the Nightmare Moon thing. I think it was still there when she returned in S1E1 and S1E2, though......I have no idea what I'm on about.

According to a wallpaper I've got on my laptop, she spent the time waiting for her sister to come back to get her, getting increasingly frightened.I figure after the first 100 years she went nuts, and boredom wasn't an issue anymore.

Nah, I think it's more that she Became the Mask as a defense mechanism.She decided she must surely be a great evil thing to deserve to be on the moon so long, so since the Pony mind is just as reliant as the human on things 'making sense', she abandoned even considering being Luna (after all, Luna did not deserve such a fate, it would not make sense for Luna to be punished so harshly) and became Nightmare Moon (who is so horrible that it was the least Celestia could do to trap her, but just they wait until she comes back, *evil laughter*)Heck, plotting Equestria's downfall would give her something to occupy her time too.

Only comics I read are webcomics.And, I suppose Donald Duck (Donald's big in Scandinavia, though Norway's the only one that seems to go with the English name, rather than something like 'Anders And')So, nope, only clues I've got is the show and people's interpretations of her.